Dynamometric screw or nut

ABSTRACT

A torque nut or screw that allows the nut to be tightened to a preset maximum torque, but prevents excess tightening. The nut or screw includes inner and outer threaded elements that extend along the same axis. The outer threaded element is tapered with respect to the axis. The fastener includes an inner fastening member (7) having fastening threads (8) and an outer female member (10) that is rotatable by means of a spanner, a pair of pliers, a screw driver, or other tool. The female member is connected to the inner fastening member by a coupling (13) having a sufficient strength to transfer to the inner fastening member a torque of a magnitude for which the fastening device is designed. The outer female member (10) is designed to be released upon tightening of the coupling and rotated relative to the inner fastening member (7), but not until the predetermined torque is exceeded. The coupling between the outer female (10) and the inner fastening member (7) includes a conical screw coupling.

TECHNICAL FIELD

The invention relates to a torque nut or torque screw, i.e. a fasteningdevice with fastening threads, i.e. threads which are operative for thefastening function of the device and with an indication means which isintegrated in the device to be released at a predetermined tighteningtorque, comprising an inner fastening member having said fasteningthreads and outside of the inner fastening member an outer female memberrotatable by means of a spanner, a pair of pliers, a screw driver, orother tool, said female member being connected to the inner fasteningmember by means of a coupling having a sufficient strength to transferto the inner fastening member a torque of the magnitude for which thefastening device is designed, and wherein the outer female member isprovided, at the tightening of the coupling, to be released and rotatedrelative to the inner fastening member but not until the predeterminedtorque is exceeded.

BACKGROUND OF THE INVENTION

It is in many situations desired to be able to tighten nuts and screwswith a certain predetermined torque. For this purpose special-type toolshave been designed which are released or which are provided with asignalling device, which is released when a set torque has beenachieved. These tools, however, are comparatively expensive and are notat hand in normal tool kits. Therefore, there is a need for torque nutsand torque screws which can be tightened by means of conventional tools,such as conventional spanners, pliers, screw drivers and the like,wherein the torque nut and the torque screw, respectively, shall be ableto take over the releasing or indication function of the dynamometrictool (torque tool).

BRIEF DISCLOSURE OF THE INVENTION

The purpose of the invention is to provide torque nuts and torque screwswhich can take over the "indication function" of the dynamometric tool,i.e. which can be tightened with a predetermined torque by means of aconventional tool. This can be achieved therein that the couplingbetween the outer female member and the inner fastening member consistsof a conical screw coupling.

The predetermined torque can be set by a certain tightening of the screwcoupling. The outer female member consists of a nut according to a firstpreferred embodiment of the invention, wherein the predetermined torqueis set by a certain tightening of the screw coupling between the outernut and the inner fastening member. The inner fastening member also mayconsist of an inner nut, wherein the inner nut, according to anembodiment, may be longer than the outer nut and extend between theouter nut in its two ends.

Further, according to a preferred embodiment, the inner fastening membermay have an outwardly directed flange or other abutment means in itsouter end, against which abutment means the outer nut is tightly screwedwith such a force that the joint between the outer nut and the innerfastening member can be released only by the application of saidpredetermined torque. The outer end of the inner fastening member, whichpreferably is designed as a flange, further may have a hexagonal outercross-section in order to provide lands for a wrench for easing off theinner fastening member when the joint shall be undone. The innerfastening member may also be provided with a hex socket for an Allen keyor with grooves for a screw driver in its outer end.

According to a modified embodiment, the fastening member comprises ahead designed as a nut with conical threads, the imaginary point of thecone being directed away from the fastening threads of the fasteningmember. In the said head there is a screw having conical threadscooperative with the conical threads in said head, wherein said screwhaving conical threads is rotatable by means of a spanner, a pair ofpliers, a screw driver or other tool. According to the same principlesas for the above described embodiments, said screw having conicalthreads is joined to the fastening member by a certain tightening of theconical screw joint in order to transfer, to the fastening member,torques of a magnitude for which the fastening member is designed, whilesaid screw having conical threads in said head is provided, whentightening the fastening member, to be released and rotated relative tothe fastening member but not until the predetermined torque is exceeded.

Further characteristic features and aspects of the invention will beapparent from the appending claims and from the following description ofsome preferred embodiments.

BRIEF DESCRIPTION OF DRAWINGS

In the following description of a preferred embodiment reference will bemade to the drawings in which

FIG. 1 illustrates, partly in section, a first preferred embodiment inwhich the inner fastening member consists of a nut;

FIG. 2 illustrates a second embodiment, in which the inner fasteningmember consists of a screw;

FIG. 3 shows a modification of the embodiment, where the inner fasteningmember consists of a screw; and

FIG. 4 illustrates still another embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In FIG. 1 there is shown a screw-nut joint consisting of a torque nut,generally designated 1, and a conventional screw 2. A pair of plates 3,4 or the like have a through-hole for the screw 2 and are clampedtogether between the screw head 6 and the torque nut 1.

More particularly, the plates 3, 4 are clamped between the screw head 6and an inner nut 7, which is included as an inner fastening means in thetorque nut 1. The inner nut 7 has normal, straight fastening threads 8,cooperative with the threads 9 of screw 2.

Outside of the inner nut 7, there is an outer female member in the formof an outer nut 10. The inner nut 7 has a longer axial extension thanthe outer nut 10 and the inner end portion 11 of it abuts theobject--the plates 3, 4--which are clamped in the joint. In the oppositeend of the inner nut there is a radially--outwardly--directed flange 12,which preferably has a hexagonal section to provide wrench lands for aconventional spanner for the undoing of the joint. The thread 13 betweenthe inner 7 and the outer nut 10 is conical, sloping towards the screwhead 6. The threads in the thread coupling 13 are cut in the samedirection as the screw threads 9, i.e. are normally right-threaded.

In the torque nut 1, according to the invention, the outer nut 10 isscrewed tightly on the inner nut 7, such that it has been brought toclose engagement with flange 12, which is possible by a properdimensioning of the diameters of the two nuts 7, 10 in sections of thethread coupling 13. Thereafter, the nut 10 has been tightened somewhatmore against the flange 12. Herein a very favourable development offorces is achieved in the joint between the two nuts 7 and 10 in thetorque nut 1.

When operated, the torque nut 1 is screwed on the screw 2 in the normalway, e.g. by means of an adjustable spanner, a monkey wrench, a ringspanner, or other type of open-ended spanner, slip joint pliers orsimilar tools. When portion 11 is well in engagement with the plate 3,the joint is tightened still more. Finally, when the torque exceeds acertain predetermined torque and the inner nut abut the plate 3 with apredetermined tightness, the outer nut 10 is eased, wherein the joint isprevented from being tightened too much. Due to the fact that the threadcoupling 13 is conical there is a correspondence between the easingtorque and the torque with which the inner nut 7 and the outer nut 10initially has been united to each other.

One can thereafter continue the rotation of the outer nut 10 on theinner nut 7 until the outer nut 10 abuts the plate 3, whereafter thejoint can be prestressed or locked by increasing the tightening of theouter nut 10. This is possible also by using the conical thread coupling13 under the condition that the axial displacement and the sloping angleof the cone are comparatively small. According to the preferredembodiment, the sloping angle should be 1°-5°, preferably 1°-3°. Itshould also be noted that the pitch of thread coupling 13 issubstantially smaller than that of the fastening threads 8.

When the joint shall be undone, the inner fastening member, i.e. theinner nut 7, is rotated by means of a conventional tool. If the flange12 is hexagonal, a conventional spanner can be used. If it is round,various types of pliers can be used.

In the embodiment shown in FIG. 2, the inner fastening member consistsof a screw 7' cooperating with a nut 6'. The screw 7' is provided withfastening threads 8' cooperative with threads 9' in the nut 6'. Theouter nut 10 is identical with a corresponding outer nut in the torquenut in the foregoing embodiment. Details having identicalcorrespondences in the above embodiment therefore have been given thesame reference numerals. For undoing the joint, the screw 7' is providedwith a hex socket 15 for an Allen key. In other respects, the functionis analogous with what has been explained with reference to theforegoing embodiment.

In the embodiment of FIG. 3, there is an inner fastening member in theform of a screw 17 cooperating with an outer nut 20. Between a screwhead 21 and the nut 20 there is provided a conical thread joint 23. Thefastening threads of screw 17 are designated 18. On screw 17 there isalso a flange 22 intended to function as an abutment against the objectwhich shall be clamped by means of a screw/nut joint in which the screw17 forms a part. The flange 22 can be said to correspond to portion 11at the embodiment according to FIG. 2. According to the embodiment, nut20, in that end which is opposite of screw 17, has an hex socket 25 foran Allen key. This is used for tightening the joint in the same manneras, according to the embodiment of FIG. 2, is used for gripping the nut10 by means of an adjustable spanner, ring spanner or the like. In otherrespects the function is analogous with what has been described withreference to the foregoing embodiments. As far as the conical shape ofthe screw head 21 is concerned, it should be mentioned that it can bemade in situ by means of an upsetting tool which is entered through thehex socket 25.

The embodiment according to FIG. 4 comprises a screw 27 with fasteningthreads 28 and a screw head 31 designed as a nut. In the nut 31 them isa screw 30 having the same function as the nuts 10 and 20, respectively,according to the foregoing embodiments. Between screw 30 and nut 31there is a conical thread coupling 33. The conicity is such that theimaginary point of the cone is turned away from the fastening threads28. In order to rotate the screw 30 there is a hex socket 35 for anAllen key in the screw 30. The surface 34 of the screw head 31 serves asan abutment against a working piece. The internally conical shape of thescrew head 31 can be achieved by pressing against the previouslyarranged screw 30.

When operated, the screw 27 is screwed tight by means of an Allen key inthe hex socket 35. When the surface 34 of screw 31 has been brought intocontact with the work piece (not shown), the joint is further tightened.Finally, when the torque exceeds a predetermined torque, the inner screw30 is eased. For this purpose the gap 30 is provided. For undoing thejoint, the screw head 31 can be used, which for this purpose is grippedby a suitable tool. The exterior of the screw head 31 for this purposecan be hexagonal or be provided with splines or the like to provideimproved wrench lands for a spanner.

I claim:
 1. A fastening device with fastening threads that include anintegral indication means that is released at a predetermined tighteningtorque, the fastening device comprising an inner fastening member (7)having said fastening threads (8) formed on the inside of the innerfastening member; an outer female member (10) that is rotatable by meansof a tool, said female member being connected to the inner fasteningmember by means of a coupling (13) having a strength to transfer to theinner fastening member a predetermined torque of a magnitude for whichthe fastening device is designed, and wherein the outer female member(10) is designed to be released and rotated relative to the innerfastening member (7) upon tightening of the coupling to a degree thatexceeds the predetermined torque, and wherein the coupling between theouter female member (10) and the inner fastening member comprises aconical screw coupling, and wherein the outer female member comprises anut having a conically threaded hole that extends from a first side ofthe nut to a second side of the nut, said inner fastening memberextending beyond said second side of the nut, and wherein thepredetermined torque is set by a certain tightening of the screwcoupling between the outer nut (10) and the inner fastening member (7).2. Fastening device according to claim 1, wherein the inner fasteningmember is an inner nut (7), and the inner nut (7) is longer than theouter nut (10).
 3. Fastening device according to claim 1, wherein theconically threaded hole in the female member has two ends and the holeincludes a thread that extends from one end of the hole to the other endof the hole.
 4. Fastening device according to claim 1, wherein the innerfastening member includes a radially outward extending flange that has amaximum radial dimension and wherein the outer female member has amaximum radial dimension that exceeds the maximum radial dimension ofthe flange so that the outer member may be readily engaged by a tool fortightening.
 5. Fastening device according to claim 2, wherein the innernut has two ends, and both of its ends extend beyond the outer nut, andwherein the outer end of the inner nut has an outwardly directedabutment (12) against which the outer nut (10) abuts and is tightlyscrewed with such a force that the joint between outer nut and the innerfastening member can be released only by the application of the saidpredetermined torque.